The present invention relates to condenser systems for steam turbines, and particularly the condenser system components for exhausting uncondensed products.
Fossil and nuclear steam turbine installations include gland steam condenser systems, composed of shell and tube heat exchangers, which serve to prevent the escape, to the atmosphere, of sealing steam from the turbine element shaft ends. Such a condenser system also functions to prevent escape to the atmosphere of high pressure leakage steam flowing along turbine inlet valve stems. Gland steam is piped from a zone between the air seal and outermost steam seal of each steam gland of the turbine elements to the condenser system. Similarly, high pressure valve stem leakage is conducted from a zone between the air seal and the outermost stem steam seal to the condenser system.
The mixture of gland steam and valve stem sealing leakage steam is condensed by heat exchange with condensate pumped from the main condenser hotwell through tubes in the gland steam condenser system. After almost all of the steam has condensed, non-condensible vapors, air, and any non-condensed water vapor are removed by a motor driven exhauster. The exhauster further establishes a vacuum in the gland condenser, as well as at the turbine element glands and valve leakoff zones.
A drain pipe at the bottom of the condenser shell conducts condensate from the condenser to a main condenser or to a drain tank.
FIG. 1 illustrates the basic components of a known system of this type. The system includes a condenser 2 having couplings for receiving steam to be condensed and a liquid coolant, which may be condensate pumped from the main condenser hotwell, and serves as the site of a heat exchange which produces the desired condensation. Condensate formed in condenser 2 is removed via a drain 4. Uncondensed products, including non-condensible vapors, air and any non-condensed water vapor, flow out of condenser 2 via an outlet pipe 6 and an exhauster inlet pipe 8 to an exhauster 10. From exhauster 10, the uncondensed products are vented via an exhauster outlet 12.
Within outlet pipe 6 there is mounted a valve 14, which may be a manually operated butterfly valve, and between pipe 6 and exhauster inlet pipe 8 there is disposed a check valve 16 serving to assure unidirectional flow of the uncondensed products. when two exhausters are used with one as a standby.
Exhauster 10 contains a rotatable member 10', typically an impeller, which is connected to the shaft 18 of an electric motor 20. Rotation of the impeller within exhauster 10 creates a low pressure within exhaust inlet pipe 8, so that uncondensed products are withdrawn from condenser 2 via outlet pipe 6 and exhauster inlet pipe 8. Butterfly valve 14 may be adjusted to provide the desired sub-atmospheric pressure level at the outlet of condenser 2 which is connected to pipe 6. Motor 20 is mounted on a stand 24. Exhauster 10 has a circular form in a plane perpendicular to that of FIG. 1 and rotation of impeller 10' within exhauster 10 produces a radial flow of uncondensed products from a central region communicating with inlet pipe 8 to a peripheral region in communication with exhauster outlet 12. Any condensate collecting in exhauster 10 may be removed via a drain fitting 26.
Frequently, a system of the type illustrated in FIG. 1 will include two exhausters, each coupled to a respective outlet pipe 6 and driven by a respective motor 20, primarily so that a back-up unit is available.
Despite the provision of drain fitting 26, there have been numerous occurrences of water collecting in the housing of exhauster 10, resulting in severe damage to rotating components within exhauster 10. In some instances, flooding has been so extensive that the water has reached the centerline of shaft 18 and has caused electrical shorting of motor 20. Such flooding has resulted from various causes, including failure to open the drain line connected to fitting 26, improperly designed drain lines, and clogging of the drain lines.
When an exhauster fails, the result is loss of vacuum at the shaft steam seals and the valve stems. Consequently, gross steam leakage can occur through the seals and into the turbine hall. The escaping seal steam can also travel along the turbine shaft and enter the oil seals, thereby contaminating the lubricating oil system